258 lines
9.7 KiB
Plaintext
258 lines
9.7 KiB
Plaintext
Linux Power Management Support
|
|
|
|
This document briefly describes how to use power management with your
|
|
Linux system and how to add power management support to Linux drivers.
|
|
|
|
APM or ACPI?
|
|
------------
|
|
If you have a relatively recent x86 mobile, desktop, or server system,
|
|
odds are it supports either Advanced Power Management (APM) or
|
|
Advanced Configuration and Power Interface (ACPI). ACPI is the newer
|
|
of the two technologies and puts power management in the hands of the
|
|
operating system, allowing for more intelligent power management than
|
|
is possible with BIOS controlled APM.
|
|
|
|
The best way to determine which, if either, your system supports is to
|
|
build a kernel with both ACPI and APM enabled (as of 2.3.x ACPI is
|
|
enabled by default). If a working ACPI implementation is found, the
|
|
ACPI driver will override and disable APM, otherwise the APM driver
|
|
will be used.
|
|
|
|
No sorry, you can not have both ACPI and APM enabled and running at
|
|
once. Some people with broken ACPI or broken APM implementations
|
|
would like to use both to get a full set of working features, but you
|
|
simply can not mix and match the two. Only one power management
|
|
interface can be in control of the machine at once. Think about it..
|
|
|
|
User-space Daemons
|
|
------------------
|
|
Both APM and ACPI rely on user-space daemons, apmd and acpid
|
|
respectively, to be completely functional. Obtain both of these
|
|
daemons from your Linux distribution or from the Internet (see below)
|
|
and be sure that they are started sometime in the system boot process.
|
|
Go ahead and start both. If ACPI or APM is not available on your
|
|
system the associated daemon will exit gracefully.
|
|
|
|
apmd: http://worldvisions.ca/~apenwarr/apmd/
|
|
acpid: http://acpid.sf.net/
|
|
|
|
Driver Interface -- OBSOLETE, DO NOT USE!
|
|
----------------*************************
|
|
|
|
Note: pm_register(), pm_access(), pm_dev_idle() and friends are
|
|
obsolete. Please do not use them. Instead you should properly hook
|
|
your driver into the driver model, and use its suspend()/resume()
|
|
callbacks to do this kind of stuff.
|
|
|
|
If you are writing a new driver or maintaining an old driver, it
|
|
should include power management support. Without power management
|
|
support, a single driver may prevent a system with power management
|
|
capabilities from ever being able to suspend (safely).
|
|
|
|
Overview:
|
|
1) Register each instance of a device with "pm_register"
|
|
2) Call "pm_access" before accessing the hardware.
|
|
(this will ensure that the hardware is awake and ready)
|
|
3) Your "pm_callback" is called before going into a
|
|
suspend state (ACPI D1-D3) or after resuming (ACPI D0)
|
|
from a suspend.
|
|
4) Call "pm_dev_idle" when the device is not being used
|
|
(optional but will improve device idle detection)
|
|
5) When unloaded, unregister the device with "pm_unregister"
|
|
|
|
/*
|
|
* Description: Register a device with the power-management subsystem
|
|
*
|
|
* Parameters:
|
|
* type - device type (PCI device, system device, ...)
|
|
* id - instance number or unique identifier
|
|
* cback - request handler callback (suspend, resume, ...)
|
|
*
|
|
* Returns: Registered PM device or NULL on error
|
|
*
|
|
* Examples:
|
|
* dev = pm_register(PM_SYS_DEV, PM_SYS_VGA, vga_callback);
|
|
*
|
|
* struct pci_dev *pci_dev = pci_find_dev(...);
|
|
* dev = pm_register(PM_PCI_DEV, PM_PCI_ID(pci_dev), callback);
|
|
*/
|
|
struct pm_dev *pm_register(pm_dev_t type, unsigned long id, pm_callback cback);
|
|
|
|
/*
|
|
* Description: Unregister a device with the power management subsystem
|
|
*
|
|
* Parameters:
|
|
* dev - PM device previously returned from pm_register
|
|
*/
|
|
void pm_unregister(struct pm_dev *dev);
|
|
|
|
/*
|
|
* Description: Unregister all devices with a matching callback function
|
|
*
|
|
* Parameters:
|
|
* cback - previously registered request callback
|
|
*
|
|
* Notes: Provided for easier porting from old APM interface
|
|
*/
|
|
void pm_unregister_all(pm_callback cback);
|
|
|
|
/*
|
|
* Power management request callback
|
|
*
|
|
* Parameters:
|
|
* dev - PM device previously returned from pm_register
|
|
* rqst - request type
|
|
* data - data, if any, associated with the request
|
|
*
|
|
* Returns: 0 if the request is successful
|
|
* EINVAL if the request is not supported
|
|
* EBUSY if the device is now busy and can not handle the request
|
|
* ENOMEM if the device was unable to handle the request due to memory
|
|
*
|
|
* Details: The device request callback will be called before the
|
|
* device/system enters a suspend state (ACPI D1-D3) or
|
|
* or after the device/system resumes from suspend (ACPI D0).
|
|
* For PM_SUSPEND, the ACPI D-state being entered is passed
|
|
* as the "data" argument to the callback. The device
|
|
* driver should save (PM_SUSPEND) or restore (PM_RESUME)
|
|
* device context when the request callback is called.
|
|
*
|
|
* Once a driver returns 0 (success) from a suspend
|
|
* request, it should not process any further requests or
|
|
* access the device hardware until a call to "pm_access" is made.
|
|
*/
|
|
typedef int (*pm_callback)(struct pm_dev *dev, pm_request_t rqst, void *data);
|
|
|
|
Driver Details
|
|
--------------
|
|
This is just a quick Q&A as a stopgap until a real driver writers'
|
|
power management guide is available.
|
|
|
|
Q: When is a device suspended?
|
|
|
|
Devices can be suspended based on direct user request (eg. laptop lid
|
|
closes), system power policy (eg. sleep after 30 minutes of console
|
|
inactivity), or device power policy (eg. power down device after 5
|
|
minutes of inactivity)
|
|
|
|
Q: Must a driver honor a suspend request?
|
|
|
|
No, a driver can return -EBUSY from a suspend request and this
|
|
will stop the system from suspending. When a suspend request
|
|
fails, all suspended devices are resumed and the system continues
|
|
to run. Suspend can be retried at a later time.
|
|
|
|
Q: Can the driver block suspend/resume requests?
|
|
|
|
Yes, a driver can delay its return from a suspend or resume
|
|
request until the device is ready to handle requests. It
|
|
is advantageous to return as quickly as possible from a
|
|
request as suspend/resume are done serially.
|
|
|
|
Q: What context is a suspend/resume initiated from?
|
|
|
|
A suspend or resume is initiated from a kernel thread context.
|
|
It is safe to block, allocate memory, initiate requests
|
|
or anything else you can do within the kernel.
|
|
|
|
Q: Will requests continue to arrive after a suspend?
|
|
|
|
Possibly. It is the driver's responsibility to queue(*),
|
|
fail, or drop any requests that arrive after returning
|
|
success to a suspend request. It is important that the
|
|
driver not access its device until after it receives
|
|
a resume request as the device's bus may no longer
|
|
be active.
|
|
|
|
(*) If a driver queues requests for processing after
|
|
resume be aware that the device, network, etc.
|
|
might be in a different state than at suspend time.
|
|
It's probably better to drop requests unless
|
|
the driver is a storage device.
|
|
|
|
Q: Do I have to manage bus-specific power management registers
|
|
|
|
No. It is the responsibility of the bus driver to manage
|
|
PCI, USB, etc. power management registers. The bus driver
|
|
or the power management subsystem will also enable any
|
|
wake-on functionality that the device has.
|
|
|
|
Q: So, really, what do I need to do to support suspend/resume?
|
|
|
|
You need to save any device context that would
|
|
be lost if the device was powered off and then restore
|
|
it at resume time. When ACPI is active, there are
|
|
three levels of device suspend states; D1, D2, and D3.
|
|
(The suspend state is passed as the "data" argument
|
|
to the device callback.) With D3, the device is powered
|
|
off and loses all context, D1 and D2 are shallower power
|
|
states and require less device context to be saved. To
|
|
play it safe, just save everything at suspend and restore
|
|
everything at resume.
|
|
|
|
Q: Where do I store device context for suspend?
|
|
|
|
Anywhere in memory, kmalloc a buffer or store it
|
|
in the device descriptor. You are guaranteed that the
|
|
contents of memory will be restored and accessible
|
|
before resume, even when the system suspends to disk.
|
|
|
|
Q: What do I need to do for ACPI vs. APM vs. etc?
|
|
|
|
Drivers need not be aware of the specific power management
|
|
technology that is active. They just need to be aware
|
|
of when the overlying power management system requests
|
|
that they suspend or resume.
|
|
|
|
Q: What about device dependencies?
|
|
|
|
When a driver registers a device, the power management
|
|
subsystem uses the information provided to build a
|
|
tree of device dependencies (eg. USB device X is on
|
|
USB controller Y which is on PCI bus Z) When power
|
|
management wants to suspend a device, it first sends
|
|
a suspend request to its driver, then the bus driver,
|
|
and so on up to the system bus. Device resumes
|
|
proceed in the opposite direction.
|
|
|
|
Q: Who do I contact for additional information about
|
|
enabling power management for my specific driver/device?
|
|
|
|
ACPI Development mailing list: acpi-devel@lists.sourceforge.net
|
|
|
|
System Interface -- OBSOLETE, DO NOT USE!
|
|
----------------*************************
|
|
If you are providing new power management support to Linux (ie.
|
|
adding support for something like APM or ACPI), you should
|
|
communicate with drivers through the existing generic power
|
|
management interface.
|
|
|
|
/*
|
|
* Send a request to all devices
|
|
*
|
|
* Parameters:
|
|
* rqst - request type
|
|
* data - data, if any, associated with the request
|
|
*
|
|
* Returns: 0 if the request is successful
|
|
* See "pm_callback" return for errors
|
|
*
|
|
* Details: Walk list of registered devices and call pm_send
|
|
* for each until complete or an error is encountered.
|
|
* If an error is encountered for a suspend request,
|
|
* return all devices to the state they were in before
|
|
* the suspend request.
|
|
*/
|
|
int pm_send_all(pm_request_t rqst, void *data);
|
|
|
|
/*
|
|
* Find a matching device
|
|
*
|
|
* Parameters:
|
|
* type - device type (PCI device, system device, or 0 to match all devices)
|
|
* from - previous match or NULL to start from the beginning
|
|
*
|
|
* Returns: Matching device or NULL if none found
|
|
*/
|
|
struct pm_dev *pm_find(pm_dev_t type, struct pm_dev *from);
|